Control of solidification structure of wear-resistant austenite-bainite polyphase steel with nodular eutectic

A new austenite-bainite polyphase steel with nodular carbides can be obtained by controlling the solidification structure of the steel melt, which only contains manganese and silicon, with modification of Si-Ca-B compound and air-hardening. The result indicates that the nodular carbide is in the eutectic form of austenite and (Fe, Mn)3C, which is formed between the austenitic dendrites during solidification due to element segregation. The modifying elements (calcium, silicon, etc.) have the following functions: (1) their chemical compounds (CaS, SiO2) are formed preferentially during solidification to act as heterogeneous nuclei for nodular eutectic crystallization, (2) the eutectic can be turned into the nodular shape after modification because of the decrease in the amount of the adsorbed impurity elements (oxygen and sulphur) and silicon enriched on the eutectic growth interface. The quantity of nodular eutectic makes up 10%–20%, with a size of 15–25 μm. The hardness and the toughness of this steel are 40–50 HRC and 20–40 J, respectively, and hence its wear-resistance can be more greatly increased than that of the austenite-manganese steel and the austenite-bainite steel. This revised version was published online in November 2006 with corrections to the Cover Date.     

BB84协议的改进方案

BB84量子密钥分发协议是基于合法用户,没有涉及到用户的身份认证问题,因此协议很容易遭受中间相遇攻击.笔者提出了一种改进方案,不仅可以解决用户的身份认证问题,还可以大大提高获得有用密钥比特的效率.     

碳化物团球化里氏体－贝氏体新型抗磨中锰钢

在中锰钢基础上，采用变质处理获得新型铸态抗磨钢：碳化物四球化典氏作－贝氏体钢它具有高强韧性、高耐磨性，是一种有广阔应用前景的新型抗磨材料．     

关于延长HN系列激光管寿命方法的研究

根据对激光器工作原理和影响激光器使用寿命的两个主要因素──激光管漏气、变形的分析，提出适当增加激光器能源泵的输出能量，可以延长激光管的使用寿命。     

2-D Terahertz Metallic Photonic Crystals in Parallel-Plate Waveguides

2-D metallic photonic crystals without defects, with point defects, and with a Fabry-Perot (F-P) defect are characterized by terahertz time-domain spectroscopy. The metal parallel-plate waveguide (PPWG) with single TEM-mode propagation is used as a tool to simulate 2-D photonic crystals in free space. The 2-D metallic photonic-crystal structures were fabricated by coating Au on an SU-8 polymer cylinder array. Wide terahertz bandgaps were observed in the photonic crystals within the PPWG. The experimental measurements have excellent agreement to 2-D photonic-crystal theory without defects. Defect modes are observed in the samples with defects and show the F-P defect has a strong localization effect     

A Two-Layer Key Establishment Scheme for Wireless Sensor Networks

In a large scale sensor network, it is infeasible to assign a unique Transport Layer Key (TLK) for each pair of nodes to provide the end-to-end security due to the huge memory cost per node. Thus, conventional key establishment schemes follow a key predistribution approach to establish a Link Layer Key (LLK) infrastructure between neighboring nodes and rely on multihop paths to provide the end-to-end security. Their drawbacks include vulnerability to the node compromise attack, large memory cost, and energy inefficiency in the key establishment between neighboring nodes. In this paper, we propose a novel key establishment scheme, called LAKE, for sensor networks. LAKE uses a t-degree trivariate symmetric polynomial to facilitate the establishment of both TLKs and LLKs between sensor nodes in a two-dimensional space, where each node can calculate direct TLKs and LLKs with some logically neighboring nodes and rely on those nodes to negotiate indirect TLKs and LLKs with other nodes. Any two end nodes can negotiate a TLK on demand directly or with the help of only one intermediate node, which can be determined in advance. As for the LLK establishment, LAKE is more secure under the node compromise attack with much less memory cost than conventional solutions. Due to the location-based deployment, LAKE is also energy efficient in that each node has direct LLKs with most neighbors without spending too much energy on the establishment of indirect LLKs with neighbors through multihop routing.     

Securing Mobile Ad Hoc Networks with Certificateless Public Keys

This paper studies key management, a fundamental problem in securing mobile ad hoc networks (MANETs). We present IKM, an ID-based key management scheme as a novel combination of ID-based and threshold cryptography. IKM is a certificateless solution in that public keys of mobile nodes are directly derivable from their known IDs plus some common information. It thus eliminates the need for certificate-based authenticated public-key distribution indispensable in conventional public-key management schemes. IKM features a novel construction method of ID-based public/private keys, which not only ensures high-level tolerance to node compromise, but also enables efficient network-wide key update via a single broadcast message. We also provide general guidelines about how to choose the secret-sharing parameters used with threshold cryptography to meet desirable levels of security and robustness. The advantages of IKM over conventional certificate-based solutions are justified through extensive simulations. Since most MANET security mechanisms thus far involve the heavy use of certificates, we believe that our findings open a new avenue towards more effective and efficient security design for MANETs     

H.264/AVC中的算术码及其改进方法

本文首先分析H.264/AVC中CABAC的主要过程,随后介绍了两种提高编码效率的改进方法,然后提出了一种新的提高编码速度的算术码快速算法。实验结果表明,本文提出的快速算法在编码效率没有明显降低的条件下,其编码速度有一定的提高,同时也不需要存储空间,从而比较适用于对实时性和存储空间要求高的场合。     

基于半监督学习的数据流分类方法

在数据流上建立有效的分类模型具有许多应用.流数据的动态性给业界提出了两个关键问题:如何监测数据流的变化;一旦发生显著变化,如何高效地组织足够的训练数据,调整无效的模型.提出了一个基于半监督学习的分类算法,较好地解决了这些问题.设计了一种识别显著变化的可靠方法;提出了一个基于naive Bayes的EM算法,利用较少的类标数据来扩大训练数据集,从而极大地降低类标数据的需求量.基于新的训练数据可以构建一个有效的分类器.实验结果证明了算法的优势.